style: ruff-format the notebooks and stac_auth helper

Run the repo-pinned ruff (0.11.5) over the notebooks so CI's
'ruff format --check' passes. No behavioural change — notebooks 02-05
re-verified green in the compose jupyterhub container after formatting.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

Author: lhoupert